Memory device adjusting duty cycle and memory system having the same

ABSTRACT

A memory device includes a clock receiver configured to receive, from a memory controller, a write clock that is used to receive write data during a data write operation, a duty monitor configured to generate first monitoring information by monitoring a duty of the write clock, and a duty adjuster configured to adjust the duty of the write clock in response to a duty control signal and output an adjusted write clock. The memory device provides the first monitoring information to the memory controller, and receives the duty control signal, generated using the first monitoring information, from the memory controller.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/564,564 filed Dec. 29, 2021, which is a continuation of U.S. patentapplication Ser. No. 17/148,915 filed Jan. 14, 2021, which iscontinuation application of U.S. patent application Ser. No. 16/230,185filed on Dec. 21, 2018, issued as U.S. Pat. No. 10,923,175 on Feb. 16,2021, which claims priority under 35 U.S.C. § 119 to Korean PatentApplication No. 10-2018-0012423, filed on Jan. 31, 2018, and KoreanPatent Application No. 10-2018-0062094, filed on May 30, 2018, in theKorean Intellectual Property Office, the disclosures of which areincorporated by reference herein in their entireties.

TECHNICAL FIELD

Exemplary embodiments of the inventive concept relate to memory devices,and more particularly, to a memory device that adjusts a duty cycle of aclock signal, and a memory system including the memory device.

DISCUSSION OF RELATED ART

Memory devices, such as low power double data rate (LPDDR) synchronousdynamic random access memory (SDRAM), may be usually used in varioustypes of electronic apparatuses, such as smartphones, tablet personalcomputers (PCs), or ultra books.

Memory devices may operate according to various specifications. Forexample, in the LPDDR specification, memory devices may receive, from amemory controller, a write clock that synchronizes with write data, ormay provide a read clock to the memory controller in synchronizationwith read data. Memory systems including such memory devices may need toefficiently manage duty errors of the write clock and the read clock.

SUMMARY

According to an exemplary embodiment of the inventive concept, a memorydevice includes a clock receiver configured to receive, from a memorycontroller, a write clock that is used to receive write data during adata write operation, a duty monitor configured to generate firstmonitoring information by monitoring a duty of the write clock, and aduty adjuster configured to adjust the duty of the write clock inresponse to a duty control signal and output an adjusted write clock.The memory device provides the first monitoring information to thememory controller, and receives the duty control signal, generated usingthe first the monitoring information, from the memory controller.

According to an exemplary embodiment of the inventive concept, a memorydevice includes a clock receiver configured to receive a clock signalfrom a memory controller, a first duty adjuster configured to receivethe clock signal from the clock receiver and perform a duty adjustmenton the received clock signal, a clock tree configured to generate one ormore write clocks that are used to receive the write data, by using theclock signal received from the first duty adjuster, one or more datareceivers each configured to receive the write data in synchronizationwith each of the one or more write clocks, one or more second dutyadjusters arranged in correspondence with the one or more data receiversand configured to adjust duties of the one or more write clocks that areprovided to the one or more data receivers, and a duty monitorconfigured to monitor a duty of at least one of the clock signal and theone or more write clocks, and provide first monitoring information, as aresult of the monitoring, to the memory controller.

According to an exemplary embodiment of the inventive concept, in amemory system including a memory controller, the memory controllerincludes one or more data transmitters configured to output write data,a write clock transmitter configured to output a write clock insynchronization with the write data, and a duty controller configured toreceive, from an external source, first monitoring informationrepresenting a result of monitoring a duty of the write clock,determine, based on the first monitoring information, whether the writeclock provided to the external source has a duty error, and generate afirst duty control signal that is used to adjust the duty of the writeclock output to the external source.

According to an exemplary embodiment of the inventive concept, a memorysystem includes a memory controller configured to transmit a writeclock, write data, and a control command for controlling a monitoringoperation and duty adjust operations, and a memory device. The memorydevice includes a signal transmission/reception block configured toreceive the write clock and the write data, and to transmit read dataand a read clock, a duty adjuster block including a plurality a dutyadjusters configured to perform the duty adjust operations and connectedto the signal transmission/reception block, a clock tree configured toreceive the write clock via the duty adjuster block, and transmit thewrite clock and the read clock based on the write clock to a pluralityof nodes in the memory device; and a first duty monitor configured toperform the monitoring operation to monitor a duty of the write clockapplied to at least one of the plurality of nodes and generate firstmonitoring information.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the inventive concept will be moreclearly understood by describing in detail exemplary embodiments thereofwith reference to the accompanying drawings.

FIG. 1 is a block diagram of a memory system including a memory device,according to an exemplary embodiment of the inventive concept.

FIG. 2 is a block diagram illustrating an operation of the memory systemof FIG. 1 according to an exemplary embodiment of the inventive concept.

FIG. 3 is a block diagram of a memory system using a mode register set(MRS), according to an exemplary embodiment of the inventive concept.

FIG. 4 is a flowchart of a method of operating a memory device,according to an exemplary embodiment of the inventive concept.

FIG. 5 is a block diagram of a memory system to which duty monitoringwith respect to a read clock has been applied according to an exemplaryembodiment of the inventive concept.

FIG. 6 is a block diagram illustrating a memory controller included inthe memory system of FIG. 5 according to an exemplary embodiment of theinventive concept.

FIG. 7 is a block diagram of a memory system according to an exemplaryembodiment of the inventive concept.

FIG. 8 is a block diagram of a memory system according to an exemplaryembodiment of the inventive concept.

FIGS. 9 and 10 are block diagrams illustrating a memory system accordingto exemplary embodiments of the inventive concept.

FIG. 11 is a flowchart of a method of operating a memory device,according to an exemplary embodiment of the inventive concept.

FIG. 12 is a table illustrating information stored in an MRS accordingto an exemplary embodiment of the inventive concept.

FIGS. 13A and 13B are circuit diagrams illustrating a duty adjuster thatperforms duty adjustment according to the information of FIG. 12according to an exemplary embodiment of the inventive concept.

FIG. 14 is a waveform diagram illustrating clock signals that are usedin a duty monitoring operation according to an exemplary embodiment ofthe inventive concept.

FIG. 15 is a block diagram of a duty monitor according to an exemplaryembodiment of the inventive concept.

FIG. 16 is a block diagram of an electronic device including a memorysystem, according to an exemplary embodiment of the inventive concept.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the inventive concept provide a memory devicecapable of efficiently adjusting a duty cycle and improving theperformance of a memory system, and a memory system including the memorydevice.

Exemplary embodiments of the inventive concept will now be describedmore fully with reference to the accompanying drawings. Like referencenumerals may refer to like elements throughout this application.

FIG. 1 is a block diagram of a memory system including a memory device,according to an exemplary embodiment of the inventive concept.

Referring to FIG. 1, a memory system 10 may include a memory controller100 and a memory device 200. The memory system 10 may be included in apersonal computer (PC) or a mobile electronic apparatus. The mobileelectronic apparatus may be implemented using a laptop computer, amobile telephone, a smartphone, a tablet PC, a personal digitalassistant (PDA), an enterprise digital assistant (EDA), a digital stillcamera, a digital video camera, a portable multimedia player (PMP), apersonal navigation device or portable navigation device (PND), ahandheld game console, a mobile Internet device (MID), a wearablecomputer, an Internet of Things (IoT) device, an Internet of Everything(IoE) device, or a drone.

The memory controller 100 may be implemented using a system on chip(SoC), an application processor (AP), a mobile AP, a chipset, or a groupof chips. For example, the memory controller 100 may be a semiconductordevice that performs a memory control function, or may be a componentincluded in an AP. For example, the AP may include the memory controller100, random access memory (RAM), a central processing unit (CPU), agraphics processing unit (GPU), and/or a modem.

The memory device 200 may be implemented using a volatile memory device.The volatile memory device may be implemented using RAM, dynamic RAM(DRAM), or static RAM (SRAM), but the inventive concept is not limitedthereto. For example, the memory device 200 may be double data ratesynchronous dynamic random access memory (DDR SDRAM), low power doubledata rate (LPDDR) SDRAM, graphics double data rate (GDDR) SDRAM, rambusdynamic random access memory (RDRAM), or the like. Alternatively, thememory device 200 may be implemented using a high bandwidth memory(HBM).

The memory device 200 may be implemented using a non-volatile memorydevice. For example, the memory device 200 may be implemented using aresistive memory, such as phase change RAM (PRAM), magnetic RAM (MRAM),or resistive RAM (RRAM).

Referring to FIG. 1, the memory controller 100 may include a dutycontroller 110. The memory device 200 may include at least one dutyadjuster (or a duty cycle adjustor) 210 and a duty monitor 220. The dutycycle adjustor may also be referred to as a duty cycle actuator. Thememory device 200 may include various components for memory operations,such as writing and reading of data. For example, the memory device 200may further include a memory cell array and its peripheral circuits. Theperipheral circuits are various components for memory operations, andthus may include various types of circuits, such as a command decoder, arow decoder, a column decoder, and a data input/output circuit.

In response to a write/read request from a host HOST, the memorycontroller 100 may control the memory device 200 such that data DQ isread from the memory device 200 or written to the memory device 200. Indetail, the memory controller 100 may control read and write operationsof the data DQ with respect to the memory device 200, by providing anaddress and a command to the memory device 200. Write data DQ and readdata DQ may be transmitted or received between the memory controller 100and the memory device 200.

The memory controller 100 may provide a clock signal, for use in a datawrite and/or read operation, to the memory device 200. Because thememory device 200 receives the write data DQ by using the clock signalreceived from the memory controller 100, the clock signal may bereferred to as a write clock WCK. The memory device 200 may performsignal processing with respect to the write clock WCK received from thememory controller 100, and thus an internal write clock may be generatedand used during reception or outputting of actual data DQ.

According to exemplary embodiments of the inventive concept, anoperation of monitoring the duty of the write clock WCK may correspondto an operation of monitoring the duty of a clock signal that is appliedto various nodes in the memory device 200. For example, the internalwrite clock generated based on the write clock WCK may be monitored. Forexample, the internal write clock may be generated such that at leastone of a frequency and a phase of the internal write clock is differentfrom the write clock WCK. A plurality of internal write clocks may begenerated based on the write clock WCK and may be used to receive onebit of data, and a duty monitoring operation may be performed withrespect to the plurality of internal write clocks.

In other words, according to an exemplary embodiment of the inventiveconcept, the duty of the write clock WCK provided by the memorycontroller 100 may be determined by monitoring the duty of the internalwrite clock. Duty monitoring operations according to exemplaryembodiments of the inventive concept may be understood as monitoring theduties of various types of clock signals, such as the write clock WCKprovided to the memory device 200 or the internal write clock generatedby the memory device 200. In other words, according to exemplaryembodiments of the inventive concept, the write clock WCK may beinterchangeably used with the internal write clock.

For example, during a data write operation, the memory device 200 mayreceive write data DQ together with the write clock WCK, insynchronization with the write clock WCK, and a data receiver within thememory device 200 may receive or latch the write data DQ by using thewrite clock WCK. During a data read operation, the memory device 200 mayinternally generate a read clock RDQS. For example, the memory device200 may generate the read clock RDQS, based on the write clock WCK. Thememory device 200 may transmit the read data DQ to the memory controller100, in synchronization with the read clock RDQS.

To improve reception performance of the write data DQ within the memorydevice 200, the duty of the write clock WCK for use in latching thewrite data DQ needs to be optimized. For example, the duty of the writeclock WCK provided by the memory controller 100 may be deformed due toan influence of a channel between the memory controller 100 and thememory device 200 or duty distortion generated within the memory device200, and reception performance of the write data DQ may be degraded dueto the deformed duty.

According to an exemplary embodiment of the inventive concept, at leastsome operations for adjusting the duty of the write clock WCK and/or theread clock RDQS may be performed in the memory controller 100. Forexample, the write clock WCK and the read clock RDQS may be used toalign data DQ that is input and output, and duty adjustment of the writeclock WCK and/or the read clock RDQS may be performed by the dutyadjuster 210 within the memory device 200. The duty of the write clockWCK and/or the read clock RDQS may be monitored by the duty monitor 220(for example, a simple monitor circuit, such as shmoo) within the memorydevice 200, and monitoring information D_Info may be provided from thememory device 200 to the memory controller 100.

For example, the duty adjuster 210 may adjust the duty of the writeclock WCK provided by the memory controller 100, and the duty monitor220 may monitor the duty of the write clock WCK that is applied to atleast one node in the memory device 200. The duty monitoring may includean operation of detecting a ratio (for example, a duty ratio) between alogic high section and a logic low section of the write clock WCK, andthe duty monitor 220 may generate the monitoring information D_Infocorresponding to the detected duty ratio of the write clock WCK. Inother words, the duty monitor 220 may generate the monitoringinformation D_Info of which a value is changed as the duty ratio of thewrite clock WCK is changed. According to an exemplary embodiment of theinventive concept, the monitoring information D_Info may have a digitalvalue including a plurality of bits, and the digital value of themonitoring information D_Info may be changed according to a result ofmonitoring the duty of the write clock WCK.

When the duty adjuster 210 adjusts the duty of the read clock RDQS thatis provided to the memory controller 100, the duty monitor 220 maymonitor the duty of the read clock RDQS that is applied to the at leastone node within the memory device 200. According to an exemplaryembodiment of the inventive concept, the memory device 200 may generateat least one read clock RDQS by using the write clock WCK received fromthe memory controller 100, and the duty monitor 220 may monitor the dutyof the generated read clock RDQS and may generate the monitoringinformation D_Info as a result of the monitoring.

The duty controller 110 of the memory controller 100 may determinewhether the duty of the write clock WCK and/or the read clock RDQS needsto be adjusted based on the monitoring information D_Info. For example,when the duty of the write clock WCK and/or the read clock RDQS is notappropriate to receive or transmit the data DQ, it may be determinedthat there is a duty error, and the duty controller 110 may provide, tothe memory device 200, a control signal Ctrl for minimizing the dutyerror. The control signal Ctrl may be provided to the duty adjuster 210within the memory device 200, and the duty adjuster 210 may adjust theduty of the write clock WCK and/or the read clock RDQS in response tothe control signal Ctrl.

According to an exemplary embodiment of the inventive concept, at leastsome functions for duty adjustment may be performed by the memorycontroller 100. For example, according to the LPDDR5 specification ofDRAM, a duty error or duty cycle error of the write clock WCK operatingat high speed is not processed within the DRAM, and a path capable ofmonitoring, comparison, and control (duty cycle adjustor DCA) via thememory controller 100 is provided, and thus, the total performance ofthe memory system 10 may be increased.

Although both duty adjustments with respect to the write clock WCK andthe read clock RDQS have been performed by a single device in FIG. 1,the respective duties of the write clock WCK and the read clock RDQS maybe independently controlled via independent duty adjusters. The writeclock WCK or the read clock RDQS of FIG. 1 may also be referred to as adata strobe signal in the memory system 10, and the duty of the datastrobe signal is monitored.

When the memory device 200 internally processes a duty error, the memorycontroller 100 has a limit in controlling the duty of the write clockWCK and/or the read clock RDQS, and it may be impossible to check aninternal margin. However, these problems may be addressed, which will bedescribed in detail below.

FIG. 2 is a block diagram illustrating an operation of the memory systemof FIG. 1 according to an exemplary embodiment of the inventive concept.Descriptions of a structure and an operation of the memory system 10shown in FIG. 2 that are the same as or similar to those provided withreference to FIG. 1 will be omitted. FIG. 2 illustrates duty monitoringand duty adjustment operations included in a data write operation, andalso illustrates, as independent components, the write clock WCKprovided from the memory controller 100 and an internal write clockWCK_I generated within the memory device 200.

Referring to FIGS. 1 and 2, the memory device 200 may include the dutyadjuster 210, the duty monitor 220, a clock receiver 230, and a datareceiver 240. The clock receiver 230 may receive from the memorycontroller 100 the write clock WCK that synchronizes with the write dataDQ and may transmit the internal write clock WCK_I to internal circuitswithin the memory device 200. For example, the clock receiver 230 maygenerate the internal write clock WCK_I via internal signal processingon the write clock WCK from the memory controller 100.

The internal write clock WCK_I generated by the clock receiver 230 maybe provided to the duty adjuster 210. The duty adjuster 210 may adjust aduty of the internal write clock WCK_I and provide a duty-adjustedinternal write clock WCK_I to the data receiver 240. The data receiver240 may receive the write data DQ in synchronization with the internalwrite clock WCK_I.

The duty monitor 220 may receive the internal write clock WCK_I from theduty adjuster 210. The internal write clock WCK_I may be transmitted viavarious paths within the memory device 200. According to an exemplaryembodiment of the inventive concept, the duty monitor 220 may beelectrically connected to an input end of the data receiver 240 and maymonitor the duty of the internal write clock WCK_I that is provided tothe data receiver 240.

According to an exemplary embodiment of the inventive concept, the writedata DQ may include a plurality of bits, and the data receiver 240 mayinclude a plurality of reception circuits in correspondence with theplurality of bits. The duty adjuster 210 may include a plurality of dutyadjusters in correspondence with the plurality of reception circuits.The internal write clock WCK_I may be provided to each of the pluralityof duty adjusters. At this time, the duty monitor 220 may monitor dutiesof at least some of the internal write clocks WCK_I that are provided tothe plurality of duty adjusters. In other words, the duty monitor 220may generate a plurality of pieces of the monitoring information D_Infocorresponding to the plurality of duty adjusters, and may provide thegenerated plurality of pieces of the monitoring information D_Info tothe memory controller 100.

According to the exemplary embodiment of FIG. 2, a feedback path may beformed between the memory controller 100 and the memory device 200, andmay include a path via which the monitoring information D_Info istransmitted. For example, the duty of the write clock WCK output by thememory controller 100 may be monitored based on the internal write clockWCK_I within the memory device 200, and a monitoring result may beprovided to the memory controller 100.

According to the exemplary embodiment of FIGS. 1 and 2, the memorycontroller 100 may determine a duty state of the write clock WCK that isused in the memory device 200, and a control operation for adjusting theduty of the write clock WCK (for example, an operation of generating acontrol signal for controlling duty adjustment) may be performed by thememory controller 100. In this case, the memory controller 100 maydetermine the necessity of adjusting the duty of the write clock WCK,and accordingly may control the memory device 200 to selectively performa duty adjust operation. For example, the memory controller 100 mayenable or disable the duty adjust operation of the memory device 200,and, when the duty adjust operation of the memory device 200 isdisabled, power consumed for duty adjustment may be reduced.

According to such an exemplary embodiment of the inventive concept, aduty adjuster (or a duty cycle actuator) enabling duty error correctionsof the write clock WCK and the read clock RDQS may be included in amemory device, and duty error information (or information obtained byduty monitoring) of the write clock WCK and the read clock RDQS may beprovided to a memory controller via a feedback path. The memorycontroller may perform a comparison operation based on receivedmonitoring information (for example, a comparison operation fordetermining whether duty adjustment is needed), and may generate acontrol signal for controlling the duty adjuster to minimize a dutyerror.

FIG. 3 is a block diagram of a memory system using a mode register set(MRS), according to an exemplary embodiment of the inventive concept.

Referring to FIG. 3, a memory system 300 may include a memory controller310 and a memory device 320, and the memory controller 310 may include aduty controller 311. The memory device 320 may include a duty adjuster321, a duty monitor 322, and an MRS 323. Detailed operations of the dutycontroller 311, the duty adjuster 321, and the duty monitor 322 are thesame as or similar to those in the above-described exemplary embodimentsof the inventive concept, and thus detailed descriptions thereof will beomitted.

Various signals may be transmitted or received between the memorycontroller 310 and the memory device 320 via various paths. For example,the memory device 320 may transmit the monitoring information D_Info tothe memory controller 310 by using a pin defined in an LPDDRxspecification, such as LPDDR4 or LPDDR5. For example, the monitoringinformation D_Info may be provided to the memory controller 310 via atleast one pin selected from among a plurality of pins defined in theLPDDRx specification. Similarly, the control signal Ctrl from the memorycontroller 310 may be provided to the memory device 320 by using atleast one pin defined in the LPDDRx specification, such as LPDDR4 orLPDDR5.

According to an exemplary embodiment of the inventive concept, the dutymonitor 322 may monitor the duty of the write clock WCK from at leastone node in the memory device 320, and may store the monitoringinformation D_Info having a plurality of bits in the MRS 323. The memorydevice 320 may include one or more pins (for example, MRS pins) forstoring information in the MRS 323 or reading information from the MRS323 via communication with the memory controller 310, and the monitoringinformation D_Info read out from the MRS 323 may be provided to thememory controller 310 via the MRS pins.

The control signal Ctrl from the memory controller 310 may be providedto the MRS 323 of the memory device 320 via the MRS pins. For example,the control signal Ctrl may be stored in the MRS 323, and the controlsignal Ctrl may be read from the MRS 323 and provided to the dutyadjuster 321. When the duty monitor 322 monitors the duty of the readclock RDQS, the monitoring information D_Info that results frommonitoring the duty of the read clock RDQS may be stored in the MRS 323,and the monitoring information D_Info read from the MRS 323 may beprovided to the memory controller 310 via the MRS pins.

FIG. 4 is a flowchart of a method of operating a memory device,according to an exemplary embodiment of the inventive concept.

Referring to FIG. 4, in operation S11, the memory device may communicatewith a memory controller, and may receive write data and a write clockthat synchronizes with the write data, together with a write commandfrom the memory controller. The memory device may include a datareceiver and a write clock receiver, and the data receiver may receivethe write data in synchronization with the write clock transmitted tothe memory device.

The memory device may include a duty monitor according to theabove-described exemplary embodiments. In operation S12, the dutymonitor may monitor the duty of the write clock (for example, aninternal write clock) output by the write clock receiver. For example,the write clock may be transmitted via various paths within the memorydevice, and the duty monitor may receive the write clock from nodes ofone or more paths and monitor the duty of the write clock.

According to an exemplary embodiment of the inventive concept, inoperation S13, the duty monitor may generate monitoring informationhaving a digital value that varies according to a variation in the dutyof the write clock, and the monitoring information generated by the dutymonitor may be transmitted to the memory controller. The memorycontroller may determine a duty ratio of the write clock within thememory device, based on the monitoring information received from thememory device, and may also determine whether the duty of the writeclock has an error (or whether the duty of the write clock needs to beadjusted). The memory controller may generate a duty control signal foradjusting the duty of the write clock within the memory device, based onthe monitoring information.

The memory device includes a duty adjuster according to theabove-described exemplary embodiments. In operation S14, the memorydevice may receive the duty control signal from the memory controller.In operation S15, the duty adjuster within the memory device may adjustthe duty of the write clock in response to the duty control signal.

FIG. 5 is a block diagram of a memory system to which duty monitoringwith respect to a read clock has been applied according to an exemplaryembodiment of the inventive concept.

Referring to FIG. 5, a memory system 400 may include a memory controller410 and a memory device 420, and the memory controller 410 may include aduty controller 411. The memory device 420 may include a write clockreceiver 421, a first duty adjuster 422, a read clock generator 423, asecond duty adjuster 424, and a duty monitor 425.

The memory controller 410 may provide the write data DQ and the writeclock WCK, together with a data write command, to the memory device 420.The write clock receiver 421 may receive the write clock WCK and providethe received write clock WCK to the first duty adjuster 422. The writeclock WCK output by the first duty adjuster 422 may be provided to adata receiver that receives the write data DQ. According to theabove-described exemplary embodiments, the duty monitor 425 may monitorthe duty of the write clock WCK output by the first duty adjuster 422(or provided to the data receiver).

As the memory controller 410 provides a read command to the memorydevice 420, the memory device 420 may transmit, to the memory controller410, the read data DQ and the read clock RDQS that synchronizes with theread data DQ. The read clock generator 423 may generate the read clockRDQS in various forms. According to an exemplary embodiment of theinventive concept, the read clock generator 423 may generate the readclock RDQS by using the write clock WCK. For example, the read clockgenerator 423 may include a clock tree that receives the write clockWCK, and the read clock RDQS from the read clock generator 423 may beprovided to the second duty adjuster 424. The memory device 420 mayfurther include a data transmitter that transmits the read data DQ, andthe data transmitter may transmit the read data DQ to the memorycontroller 410 in synchronization with the read clock RDQS from the readclock generator 423 or the second duty adjuster 424.

According to an exemplary embodiment of the inventive concept, the dutymonitor 425 may further generate a result of monitoring the duty of theread clock RDQS. For example, the duty monitor 425 may receive the readclock RDQS from the read clock generator 423 or the second duty adjuster424, and may monitor the duty of the read clock RDQS to generate amonitoring result. Accordingly, the duty monitor 425 may provide bothfirst monitoring information D_Info_W about the write clock WCK andsecond monitoring information D_Info_R about the read clock RDQS to thememory controller 410.

The duty controller 411 may output a first duty control signal Ctrl_Wfor adjusting the duty of the write clock WCK, based on the firstmonitoring information D_Info_W about the write clock WCK. The dutycontroller 411 may also output a second duty control signal Ctrl_R foradjusting the duty of the read clock RDQS, based on the secondmonitoring information D_Info_R about the read clock RDQS. The secondduty adjuster 424 may adjust the duty of the read clock RDQS in responseto the second duty control signal Ctrl_R.

According to such an exemplary embodiment of the inventive concept, whenthe memory controller 410 receives the read data DQ from the memorydevice 420, the duty of the read clock RDQS that synchronizes with theread data DQ does not need to be adjusted within the memory controller410, and the memory controller 410 may receive the read clock RDQShaving a duty optimized for reception of the read data DQ from thememory device 420.

For example, if data reception performance is optimized where the memorycontroller 410 receives the read clock RDQS in which a logic highsection and a logic low section have a ratio of 50 to 50, even when thememory device 420 outputs the read clock RDQS having such an optimalduty ratio, the duty ratio of the read clock RDQS may be changed due toan influence of a channel between the memory controller 410 and thememory device 420. In this case, reception performance of the read dataDQ of the memory controller 410 may be reduced.

However, according to an exemplary embodiment of the inventive concept,the memory device 420 may adjust the duty of the read clock RDQS, basedon the second duty control signal Ctrl_R in which the influence of thechannel has been reflected, and the memory controller 410 may receivethe read data DQ in synchronization with the read clock RDQS having anoptimized duty.

FIG. 6 is a block diagram illustrating a memory controller included inthe memory system of FIG. 5 according to an exemplary embodiment of theinventive concept.

Referring to FIGS. 5 and 6, the memory controller 410 may include theduty controller 411 and a duty monitor 412. According to theabove-described exemplary embodiment of the inventive concept, the dutycontroller 411 may output the first duty control signal Ctrl_W foradjusting the duty of the write clock WCK, and the second duty controlsignal Ctrl_R for adjusting the duty of the read clock RDQS.

The memory controller 410 may receive from the memory device 420 theread data DQ and the read clock RDQS synchronized with the read data DQ,and may latch the read data DQ in synchronization with the read clockRDQS. The duty monitor 412, for monitoring the duty of a clock signal asdescribed above, may receive the read clock RDQS, and the duty of theread clock RDQS may be monitored in the memory controller 410.

The duty controller 411 may generate the second duty control signalCtrl_R by using at least one of the second monitoring informationD_Info_R from the memory device 420 and third monitoring informationRes_Mor from the duty monitor 412. For example, the duty controller 411may selectively use one of the second monitoring information D_Info_Rand the third monitoring information Res_Mor, or may generate the secondduty control signal Ctrl_R by using a combination of the secondmonitoring information D_Info_R and the third monitoring informationRes_Mor. For example, when a duty error is determined from at least oneof the second monitoring information D_Info_R and the third monitoringinformation Res_Mor, the duty of the read clock RDQS may be adjusted byoutputting the second duty control signal Ctrl_R.

FIG. 7 is a block diagram of a memory system according to an exemplaryembodiment of the inventive concept. FIG. 7 illustrates DRAM as a memorydevice as an example in which duty monitoring is performed on a writeclock and a read clock.

Referring to FIG. 7, a memory system 500 may include a memory controller510 and a memory device 520, and each of the memory controller 510 andthe memory device 520 may include various components related with amemory operation. For example, the memory controller 510 may include aclock signal transmitter 512, a data transmitter 513, a data receiver514, a read clock receiver 515, and a duty controller 511.

The memory device 520 may include a write clock receiver 521 forreceiving the write clock WCK, a data receiver 522 for receiving thewrite data DQ, a data transmitter 523 for transmitting the read data DQ,and a read clock transmitter 524 for transmitting the read clock RDQS.When the memory device 520 receives the write data DQ having a pluralityof bits in parallel, the data transmitter 513 of the memory controller510 may include a plurality of transmission circuits, and the datareceiver 522 of the memory device 520 may include a plurality ofreception circuits. When the memory device 520 outputs the read data DQhaving a plurality of bits in parallel, the data receiver 514 of thememory controller 510 may include a plurality of reception circuits, andthe data transmitter 523 of the memory device 520 may include aplurality of transmission circuits.

The memory device 520 may further include one or more duty adjusters525_1 through 525_4, a clock tree 526, and a duty monitor 527. In a sameor similar manner as or to the above-described exemplary embodiments,each of the duty adjusters 525_1 through 525_4 may perform a duty adjustoperation on a received clock signal in response to control signalsCtrl_W and Ctrl_R received from the memory controller 510. According tothe above-described exemplary embodiments, the duty monitor 527 maymonitor the duty of the clock signal that is applied to at least onenode within the memory device 520, and generate monitoring informationas a result of the monitoring. For example, the monitoring informationmay have a digital value of m bits (m_bit).

A data receiver included in each of the memory controller 510 and thememory device 520 may include a flip-flop that latches data DQ insynchronization with a clock signal. For example, the data receiver 514of the memory controller 510 may latch the read data DQ in response tothe read clock RDQS, and the data receiver 522 of the memory device 520may latch the write data DQ in response to the write clock WCK.

According to an exemplary embodiment of the inventive concept, the dutyadjusters 525_1 through 525_4 may be arranged in correspondence with theabove-described various transmitters and receivers. For example, theduty adjusters 525_1 through 525_4 may include the duty adjuster 525_1adjusting the duty of the write clock WCK output by the write clockreceiver 521, the duty adjuster 525_2 adjusting the duty of the writeclock WCK provided to the data receiver 522, the duty adjuster 525_3adjusting the duty of the read clock RDQS provided to the datatransmitter 523, and the duty adjuster 525_4 adjusting the duty of theread clock RDQS provided to the read clock transmitter 524. As describedabove, when each of the write data DQ and the read data DQ includes aplurality of bits, the duty adjuster 525_2 may include a plurality ofduty adjusters in correspondence with the plurality of receptioncircuits, and the duty adjuster 525_3 may include a plurality of dutyadjusters in correspondence with the plurality of transmission circuits.

The write clock WCK may be provided to the clock tree 526 and may beprovided to various nodes within the memory device 520 via the clocktree 526. The duty monitor 527 may monitor the duties of the write clockWCK and the read clock RDQS via the various nodes within the memorydevice 520. For example, FIG. 7 illustrates an example in which the dutymonitor 527 monitors the duty of the write clock WCK via a node a andmonitors the duty of the read clock RDQS via a node b.

The write clock WCK may be provided to the data receiver 522 via thenode a and may be used to latch the write data DQ. At this time, theduty monitor 527 may monitor the duty of the write clock WCK to providethe first monitoring information D_Info_W. For example, the firstmonitoring information D_Info_W may include m bits of information.

During a data read operation, a signal based on the write clock WCK maybe provided as the read clock RDQS to the read clock transmitter 524 viathe clock tree 526, and the read clock transmitter 524 may transmit theread clock RDQS to the memory controller 510. The duty monitor 527 mayprovide the second monitoring information D_Info_R including m bits ofinformation by monitoring the duty of the read clock RDQS.

Although FIG. 7 illustrates an example in which the duties of the writeclock WCK and the read clock RDQS are monitored via the nodes a and b,the inventive concept is not limited thereto. As described above, theduties of the write clock WCK and the read clock RDQS may be monitoredvia the various nodes within the memory device 520. For example, theduty of the write clock WCK output by the duty adjuster 525_1 may bemonitored via a node c. For example, because the write clock WCKprovided to the data receiver 522 to receive the write data DQ and theread clock RDQS provided to the data transmitter 523 to output the readdata DQ may be generated from the clock tree 526, based on the writeclock WCK output by the duty adjuster 525_1, a result of duty monitoringof the write clock WCK output by the duty adjuster 525_1 may be commonlyused to adjust the duties of the write clock WCK and the read clockRDQS.

To monitor the duty of the read clock RDQS, the duty of the read clockRDQS output by the clock tree 526 via a node d may be monitored, or theduty of the read clock RDQS output by the duty adjuster 525_3 via a nodee may be monitored.

The duty controller 511 of the memory controller 510 may detect dutyerrors of the write clock WCK and the read clock RDQS, based on receivedpieces of the monitoring information D_Info_W and D_Info_R, and mayprovide the control signal Ctrl for minimizing a duty error to thememory device 520. For example, the duty controller 511 may generate thefirst duty control signal Ctrl_W, based on the first monitoringinformation D_Info_W about the write clock WCK, and the first dutycontrol signal Ctrl_W may be provided to duty adjusters (for example,525_1 and 525_2) that adjust the duty of the write clock WCK.

The duty controller 511 may also generate the second duty control signalCtrl_R, based on the second monitoring information D_Info_R about theread clock RDQS. For example, the duty controller 511 may generate thesecond duty control signal Ctrl_R by using the second monitoringinformation D_Info_R, and the second duty control signal Ctrl_R may beprovided to duty adjusters (for example, 525_3 and 525_4) that adjustthe duty of the read clock RDQS. Alternatively, as in theabove-described embodiment of the inventive concept, the duty controller511 may generate the second duty control signal Ctrl_R by directlymonitoring the duty of the read clock RDQS. Alternatively, the dutycontroller 511 may generate the second duty control signal Ctrl_R, basedon a combination of a result of autonomously monitoring the duty of theread clock RDQS with the second monitoring information D_Info_R providedby the memory device 520.

A duty monitoring operation according to an exemplary embodiment of theinventive concept may be performed in various ways without limiting thecomponents of FIG. 7 to operations and configurations as describedabove. For example, monitoring may be performed via the various nodeswithin the memory device 520, and the duty adjusters 525_1 through 525_4may be grouped in various ways and may perform a duty adjust operation.For example, the duty of a clock signal of a node corresponding to eachof the duty adjusters 525_1 through 525_4 may be monitored, and, basedon this, each of the duty adjusters 525_1 through 525_4 may perform aduty adjust operation in response to a separate control signal.Alternatively, the duty adjusters 525_1 through 525_4 may be groupedinto duty adjusters (for example, 525_1 and 525_2) related with a datawrite operation and duty adjusters (for example, 525_3 and 525_4)related with a data read operation, the duty of a clock signal of a nodecorresponding to each group may be monitored, and each group of the dutyadjusters 525_1 through 525_4 may perform a duty adjust operation.

Alternatively, because the write clock WCK is provided to the memorydevice 520 via the duty adjuster 525_1 as described above, the duty ofonly a clock signal of one node connected to the duty adjuster 525_1 maybe monitored, and accordingly the memory device 520 may be realized in aform that controls a duty adjust operation of only the duty adjuster525_1.

FIG. 8 is a block diagram of a memory system according to an exemplaryembodiment of the inventive concept. FIG. 8 illustrates an example inwhich a memory controller controls a period and/or enabling of a dutymonitoring operation. Detailed descriptions of components and operationsof a memory system 600 of FIG. 8 that are the same as or similar tothose given above with reference to the above-described exemplaryembodiments will not be repeated herein.

Referring to FIG. 8, the memory system 600 may include a memorycontroller 610 and a memory device 620. The memory controller 610 mayinclude a duty controller 611, a duty monitor 612, a clock signaltransmitter 613, a data transmitter 614, a data receiver 615, a readclock receiver 616, and a command transmitter 617. The memory device 620may include a signal transmission/reception block 621, a duty adjusterblock 622, a clock tree 623, a duty monitor 624, an MRS 625, a dutyadjuster controller 626, a command receiver 627, and a duty monitorcontroller 628. As described above in the above-described exemplaryembodiment of the inventive concept, the signal transmission/receptionblock 621 may include a receiver that receives the write clock WCK, areceiver that receives the write data DQ, a transmitter that outputs theread data DQ, and a transmitter that outputs the read clock RDQS.

In the case that P bits of data DQ are transmitted or received inparallel, the receiver that receives the write data DQ may include Preception circuits, and the transmitter that outputs the read data DQmay include P transmission circuits. P duty adjusters DCA_2[1:P] may bearranged in correspondence with the P reception circuits, and P dutyadjusters DCA_3 [1:P] may be arranged in correspondence with the Ptransmission circuits. Although FIG. 8 illustrates an example in whichthe duty monitor 624 is connected to an output terminal of the clocktree 623 and performs monitoring, the duty monitor 624 may performmonitoring via various nodes within the memory device 620, as describedabove.

According to the above-described exemplary embodiments, the MRS 625 maystore the monitoring information D_Info obtained by monitoring the dutyof the write clock WCK and/or the duty of the read clock RDQS, and alsostore the control signal Ctrl provided by the memory controller 610. Theduty adjuster controller 626 may control the duty adjuster block 622,based on the monitoring information D_Info read from the MRS 625, andthe duty adjusters included in the duty adjuster block 622 may performduty adjust operations under the control of the duty adjuster controller626.

The memory controller 610 may determine whether a clock signal has anoptimal duty, based on the monitoring information D_Info, and, accordingto a result of the determination, may output a control command CMD forcontrolling a monitoring operation and a duty adjust operation performedin the memory device 620. The duty monitor controller 628 may control anoperation of the duty monitor 624, in response to the control commandCMD. According to an exemplary embodiment of the inventive concept, thememory device 620 may include a command decoder for controlling a memoryoperation by decoding various types of commands from the memorycontroller 610, and the duty monitor controller 628 may be a componentcorresponding to the command decoder or may be included in the commanddecoder.

The duty monitor controller 628 may control an operation of the dutymonitor 624 in response to the control command CMD according to variousmethods. For example, when the duty of the clock signal is appropriatefor latching data, the duty monitor 624 may set a period of dutymonitoring to be long or may disable the duty monitoring under thecontrol of the duty monitor controller 628. The memory controller 610may check the monitoring information D_Info stored in the MRS 625according to a period longer than the set period, and may output thecontrol signal Ctrl, based on the checked monitoring information D_Info.Alternatively, the memory controller 610 may enable a duty monitoringoperation at a specific time point or an arbitrary time point after aduty monitoring operation in the memory device 620 is disabled, and maygenerate and output the control signal Ctrl according to theabove-described exemplary embodiments.

FIGS. 9 and 10 are block diagrams illustrating a memory system accordingto exemplary embodiments of the inventive concept.

Referring to FIG. 9, a memory system 700 may include a memory controller710 and a memory device 720, and the memory controller 710 may include aduty controller 711. The memory device 720 may include a write dutyadjuster block 721 including one or more duty adjusters for adjustingthe duty of the write clock WCK, a read duty adjuster block 722including one or more duty adjusters for adjusting the duty of the readclock RDQS, and a duty monitor 723. As described above, the write clockWCK may be provided to the memory device 720, the read clock RDQS may beprovided to the memory controller 710, and data DQ may be exchangedbetween the memory controller 710 and the memory device 720.

A plurality of duty adjusters within the memory device 720 may begrouped into the write duty adjuster block 721 and the read dutyadjuster block 722. The duty monitor 723 may monitor the duties of thewrite clock WCK and the read clock RDQS via nodes related with the writeduty adjuster block 721 and the read duty adjuster block 722, generatethe first monitoring information D_Info_W about the write clock WCK andthe second monitoring information D_Info_R about the read clock RDQS,and provide the generated first monitoring information D_Info_W and thegenerated second monitoring information D_Info_R to the memorycontroller 710. The duty controller 711 may provide the above-describedfirst duty control signal Ctrl_W and the above-described second dutycontrol signal Ctrl_R to the memory device 720. A plurality of dutyadjusters within the write duty adjuster block 721 may perform a dutyadjust operation in response to the first duty control signal Ctrl_W,and a plurality of duty adjusters within the read duty adjuster block722 may perform a duty adjust operation in response to the second dutycontrol signal Ctrl_R.

Referring to FIG. 10, a memory system 800 may include a memorycontroller 810 and a memory device 820, wherein the memory controller810 may include a duty controller 811 and the memory device 820 mayinclude a plurality of (for example, A) write duty adjusters DCA_W1through DCA_WA, a plurality of (for example, B) read duty adjustersDCA_R1 through DCA_RB, and a duty monitor 823.

The duty monitor 823 may monitor the duties of the write clock WCK andthe read clock RDQS via a node (for example, a node connected to anoutput terminal of a duty adjuster) related with each of the write dutyadjusters DCA_W1 through DCA_WA and the read duty adjusters DCA_R1through DCA_RB, and generate monitoring information as a result of themonitoring. Accordingly, the monitoring information may include aplurality of pieces of first monitoring information D_Info_W(1˜A)related with the A write duty adjusters DCA_W1 through DCA_WA and aplurality of pieces of second monitoring information D_Info_R(1˜B)related with the B read duty adjusters DCA_R1 through DCA_RB. The dutycontroller 811 of the memory controller 810 may generate the first andsecond duty control signals Ctrl_W and Ctrl_R for controlling the writeduty adjusters DCA_W1 through DCA_WA and the read duty adjusters DCA_R1through DCA_RB, based on the pieces of the first and second monitoringinformation D_Info_W(1˜A) and D_Info_R(1˜B).

FIG. 11 is a flowchart of a method of operating a memory device,according to an exemplary embodiment of the inventive concept. FIG. 11illustrates an example in which the memory device monitors the duties ofa write clock and a read clock.

Referring to FIG. 11, in operation S21, the memory device maycommunicate with a memory controller, and may receive write data and awrite clock that synchronizes with the write data from the memorycontroller, together with a write command from the memory controller.The memory device may generate various types of clock signals that areused therein, via processing with respect to the write clock. Forexample, in operation S22, the memory device may generate a read clockfrom the write clock.

The memory device may include a duty monitor that monitors the duty ofthe clock signal, and the duty monitor may receive the write clock andthe read clock from at least some of various nodes in the memory device.In operation S23, the duty monitor may monitor the duties of the writeclock and the read clock according to the above-described exemplaryembodiments. In operation S24, the memory device may transmit, to thememory controller, first monitoring information obtained by monitoringthe duty of the write clock, and second monitoring information obtainedby monitoring the duty of the read clock. In operation S25, the memorydevice may receive, from the memory controller, a write clock controlsignal generated based on a first monitoring result and also a readclock control signal generated based on a second monitoring result. Inoperation S26, the memory device may include a duty adjuster accordingto the above-described exemplary embodiments, and the memory device mayadjust the duties of the write clock and the read clock in response tothe control signals received from the memory controller.

FIG. 12 is a table illustrating information stored in an MRS accordingto an exemplary embodiment of the inventive concept, and FIGS. 13A and13B are circuit diagrams illustrating a duty adjuster that performs dutyadjustment according to the information of FIG. 12 according to anexemplary embodiment of the inventive concept.

Referring to FIG. 12, the MRS may store duty monitoring information anda control signal in a plurality of fields OP[0] through OP[n+2]. Forexample, first fields OP[n+1] and OP[n+2] from among the plurality offields OP[0] through OP[n+2] may store duty monitoring informationaccording to the above-described exemplary embodiments, and theremaining second fields OP[0] through OP[n] may store a control signalaccording to the above-described exemplary embodiments.

For example, a duty monitor within a memory device may monitor the dutyof a clock signal, such as a write clock and/or a read clock, and storemonitoring information corresponding to two bits in the first fieldsOP[n+1] and OP[n+2]. For example, when a logic low section of the clocksignal is greater than a logic high section thereof, a value of “1” maybe stored in the field OP[n+2], and when the logic high section of theclock signal is greater than the logic low section thereof, a value of“1” may be stored in the field OP[n+1].

The memory controller may receive monitoring information of the firstfields OP[n+1] and OP[n+2] and may generate a control signalcorresponding to n bits, based on the received monitoring information.Because the control signal corresponding to n bits is able to controlthe amount of duty adjustment of the clock signal, the control signalmay be referred to as a DCA weight. When the logic low section of theclock signal is greater than the logic high section thereof, the DCAweight may include control information for increasing the logic highsection of the clock signal, and, when the logic high section of theclock signal is greater than the logic low section thereof, the DCAweight may include control information for increasing the logic lowsection of the clock signal. For example, at least one bit in the DCAweight may include polarity information representing whether to increasethe duty of the logic high section or the duty of the logic low section.FIG. 12 illustrates an example in which the field OP[n] stores polarityinformation (DCA polarity).

FIGS. 13A and 13B illustrate an example in which the duty of the writeclock WCK is adjusted. Referring to FIGS. 13A and 13B, the duty of thewrite clock WCK may be adjusted according to the DCA weight stored inthe second fields OP[0] through OP[n] in various ways. For example,referring to FIG. 13A, the duty adjuster may include a plurality oftransistors connected to one another in parallel, and switching of theplurality of transistors may be controlled according to the DCA weight.For example, FIG. 13A illustrates an example in which duty adjustment isperformed due to adjustment of the size of a transistor according to theDCA weight.

As enable signals ON and ONB are activated, a duty adjust operation maybe performed, and, as the size of a transistor through which a currentpasses is adjusted according to the DCA weight, the duty of the writeclock WCK may be adjusted.

Referring to FIG. 13B, current sources may be arranged in correspondencewith the plurality of transistors, and some of the plurality oftransistors may be turned on according to the DCA weight. The amounts ofcurrent respectively flowing through output terminals OUT and OUTB maychange according to turning-on states of the transistors, andaccordingly the duty of the write clock WCK may be adjusted.

FIG. 14 is a waveform diagram illustrating clock signals that are usedin a duty monitoring operation according to an exemplary embodiment ofthe inventive concept, and FIG. 15 is a block diagram of a duty monitoraccording to an exemplary embodiment of the inventive concept.

Referring to FIGS. 14 and 15, a write clock (for example, an externalwrite clock EXT_WCK) provided by a memory controller may undergo aninternal processing operation within a memory device, and at least oneinternal write clock may be generated from the external write clockEXT_WCK. FIG. 14 illustrates two internal write clocks WCK/2_0 andWCK/2_90, each having a frequency that is half of that of the externalwrite clock EXT_WCK and having different phases from each other, and awrite command of the memory controller may be latched using the internalwrite clocks WCK/2_0 and WCK/2_90.

Duty monitoring operations according to exemplary embodiments of theinventive concept may be performed using the internal write clocksWCK/2_0 and WCK/2_90. For example, the internal write clocks WCK/2_0 andWCK/2_90 may be provided to the duty monitor, and the duty monitor mayinclude a plurality of delay circuits and a plurality of comparators.The internal write clocks WCK/2_0 and WCK/2_90 may be sequentiallydelayed via the plurality of delay circuits, and clock signals outputvia the delay circuits may be compared with one another.

For example, the duty of the external write clock EXT_WCK may bemonitored by comparing logic states of the internal write clocks WCK/2_0and WCK/2_90 with each other while adjusting delays of the internalwrite clocks WCK/2_0 and WCK/2_90. A comparison result when a logic highsection of the external write clock EXT_WCK is greater than a logic lowsection thereof, and a comparison result when the logic low section isgreater than the logic high section may have different values. Acomparison result of i comparers may be provided to a duty decider, andthe duty decider may generate the monitoring information D_Infoaccording to the above-described exemplary embodiment by using thecomparison result.

FIG. 16 is a block diagram of an electronic device including a memorysystem, according to an exemplary embodiment of the inventive concept.

An electronic device 900 may correspond to a data processing system andmay include an AP 910 and a memory device 920. The AP 910 may beimplemented by using a system on chip (SoC). The SoC may include asystem bus to which a protocol having a certain bus standard has beenapplied and may include various types of Intellectual Property (IP)devices that are connected to the system bus. An AdvancedMicrocontroller Bus Architecture (AMBA) protocol by Advanced RISCMachine (ARM) may be applied as a standard of the system bus. Examplesof buses using the AMBA protocol may include an AdvancedHigh-Performance Bus (AHB), an Advanced Peripheral Bus (APB), anAdvanced eXtensible Interface (AXI), AXI4, and AXI Coherency Extensions(ACE). Besides them, other types of protocols, such as uNetwork bySONICs Inc., CoreConnect by IBM, and an Open Core Protocol by OCP-IP,are also applicable.

The AP 910 may include a memory control module 911, a processor 912(such as, a central processing device), and an operation memory 913.Although FIG. 16 illustrates the single processor 912, the AP 910 mayinclude various types of processors. The operation memory 913 may storeinstructions for controlling overall operations of the electronic device900. The AP 910 may further include a modem processor as a component forcontrolling a modem communication function. In this case, the AP 910 maybe referred to as ModAP.

According to the above-described exemplary embodiments, the memorycontrol module 911 may include a duty controller 911_1, and the memorydevice 920 may include a cell array 921, a duty adjuster 922, and a dutymonitor 923. The memory device 920 may perform the duty monitoringoperations according to the above-described exemplary embodiments, andthe duty monitor 923 may monitor the duty of the write clock WCK and/orthe duty of the read clock RDQS, and generate the monitoring informationD_Info as a result of the monitoring. According to the above-describedexemplary embodiments, the memory control module 911 may generate thecontrol signal Ctrl for optimizing the duty of a clock signal, based onthe monitoring information D_Info, and the duty adjuster 922 of thememory device 920 may perform a duty adjust operation in response to thecontrol signal Ctrl.

While the inventive concept has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made thereto without departing from the spirit and scopeof the inventive concept as set forth by the following claims.

What is claimed is:
 1. A method for performing a duty adjustmentoperation in a memory system, the method comprising: performing a firstduty adjustment operation on a write clock, the first duty adjustmentoperation including: transmitting, by a memory controller, the writeclock to a synchronous dynamic random access memory (SDRAM) device;performing a first duty monitoring operation on the write clock togenerate a first duty monitoring information and transmitting the firstduty monitoring information to the memory controller; and adjusting aduty cycle of the write clock based on the first duty monitoringinformation; and performing a second duty adjustment operation on a readclock, the second duty adjustment operation including: generating, bythe SDRAM device, the read clock based on the write clock andtransmitting the read clock to the memory controller; performing asecond duty monitoring operation on the read clock to generate a secondduty monitoring information and transmitting the second duty monitoringinformation to the memory controller; and adjusting a duty cycle of theread clock based on the second duty monitoring information.
 2. Themethod of claim 1, wherein the memory controller variably controls aperiod of the first and second duty monitoring operation based on thefirst and second duty monitoring information.
 3. The method of claim 2,wherein the memory controller increases the period of the first andsecond duty monitoring operation when the first and second dutymonitoring information indicates that the duty error of the write clockis within a predetermined range.
 4. The method of claim 2, wherein thememory controller temporarily disables the first duty monitoringoperation and the second duty monitoring operation when the first andsecond duty monitoring information indicates that the duty error of thewrite clock is within a predetermined range.
 5. The method of claim 1,wherein the write clock continuously toggles throughout the first andsecond duty adjustment operation.
 6. The method of claim 1, wherein thefirst and second duty monitoring information stored in a first moderegister set (MRS) is transmitted to the memory controller through anMRS read operation.
 7. The method of claim 6, wherein the first MRSincludes a plurality of fields for storing the first and second dutymonitoring information, and at least one of the fields indicates whethera logic high portion of the write clock is wider than a logic lowportion of the write clock.
 8. The method of claim 7, wherein a secondMRS includes a plurality of fields indicating a duty cycle adjustmentweight.
 9. The method of claim 8, wherein at least one field of thesecond MRS indicates a polarity of the duty cycle adjustment with whichthe SDRAM device decides whether to increase a portion of the logiclevel high of the write clock or to increase a portion of the logiclevel low of the write clock.
 10. The method of claim 1, furtherperforming a write operation or a read operation after completing thefirst and second duty adjustment operation.
 11. A method for performinga duty adjustment operation in a memory system, the method comprising:transmitting, by a memory controller, a write clock to a synchronousdynamic random access memory (SDRAM) device; performing, by the SDRAMdevice, a duty monitoring operation on the write clock, and therebystoring a duty monitoring information in a first mode register set(MRS); transmitting, by the SDRAM device, the duty monitoringinformation to the memory controller; generating, by the memorycontroller, a duty control signal based on the duty monitoringinformation and transmitting the duty control signal to the SDRAMdevice; storing the duty control signal in a second MRS of the SDRAMdevice; and performing, by the SDRAM device, the duty adjustmentoperation on the write clock using the duty control signal stored in thesecond MRS, wherein the duty control signal includes a duty cycleadjustment weight which comprises at least two bits and an amount of theduty cycle adjustment is changed based on the value of the at least twobits.
 12. The method of claim 11, wherein the memory controller variablycontrols a period of the duty monitoring operation based on the dutymonitoring information.
 13. The method of claim 12, wherein the memorycontroller increases the period of the duty monitoring operation whenthe duty monitoring information indicates that a duty error of the writeclock is within a predetermined range.
 14. The method of claim 11,wherein the memory controller temporarily disables the duty monitoringoperation when the duty monitoring information indicates that a dutyerror of the write clock is within a predetermined range.
 15. The methodof claim 14, wherein the first MRS comprises a plurality of fields forstoring the duty monitoring information, and at least one of the fieldsstores a logic value indicating whether a logic high portion of thewrite clock is wider than a logic low portion of the write clock. 16.The method of claim 14, wherein both the write clock and the read clockcontinuously toggle throughout the duty adjustment operation.
 17. Themethod of claim 14, wherein the duty monitoring information stored inthe first MRS is transmitted to the memory controller through an MRSread operation.
 18. The method of claim 17, wherein the first MRSincludes a plurality of fields for storing the duty monitoringinformation, and at least one of the fields indicates whether a logichigh portion of the write clock is wider than a logic low portion of thewrite clock.
 19. The method of claim 14, wherein at least one field ofthe second MRS indicates a polarity of the duty cycle adjustment withwhich the SDRAM device decides whether to increase a portion of a logiclevel high of the write clock or to increase a portion of a logic levellow of the write clock.
 20. The method of claim 14, further performing awrite operation after completing the duty adjustment operation.